<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<input type="text" id="i1">
<input type="text" id="i2">
<input type="button" value="加" onclick="f1()">
<input type="button" value="减" onclick="f2()">
<input type="button" value="乘" onclick="f3()">
<input type="button" value="除" onclick="f4()">
<div>结果:</div>

<script>
    let i1 = document.querySelector("#i1");
    let i2 = document.querySelector("#i2");
    let d = document.querySelector("div");
    function f1(){
        if(isNaN(i1.value)||isNaN(i2.value)){
            d.innerText="输入错误";
            return;
        }
        d.innerText = "结果:"+(parseFloat(i1.value)+parseFloat(i2.value));
    }
    function f2() {
        d.innerText = "结果:"+(i1.value*1 - i2.value*1);
    }
    function f3() {
        d.innerText = "结果:"+(i1.value * i2.value);
    }
    function f4() {
        d.innerText = "结果:"+(i1.value / i2.value );
    }

</script>

</body>
</html>